Magnesium PPM Calculator
Yellow leaves with green veins? That is magnesium deficiency — the chlorophyll molecule literally has magnesium at its center. Target 30–70 PPM and the color comes back.
Calculator
Magnesium PPM Calculator
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Yellow leaves with green veins? That is magnesium deficiency — the chlorophyll molecule literally has magnesium at its center. Target 30–70 PPM and the color comes back.
How to use this calculator
- Enter volume.
- Enter target Mg PPM.
- Enter fertilizer Mg%.
- Get grams (Epsom salt is 9.8% Mg).
The formula
Epsom salt (magnesium sulfate) is the common source at ~9.8% Mg.
What the inputs mean
The target is the concentration you want, in PPM. The volume is how much liquid you are treating. The magnesium content (%) corrects for product strength, because most products are not 100% active ingredient. The result tells you exactly how much magnesium fertilizer to add.
Worked example
100 L, 50 PPM Mg via Epsom salt: 50 × 100 ÷ 1,000 ÷ 0.098 ≈ 51 g.
Quick reference
| Source | Mg % |
|---|---|
| Epsom salt | 9.8% |
| Magnesium nitrate | 9.5% |
Common Mg sources.
Where you will actually use this
Mg deficiency mimics other problems; dosing by PPM removes the guesswork.
- Correcting Mg deficiency
- Routine hydroponic feeding
- Foliar-adjacent programs
Mistakes that give wrong answers
- High K blocking Mg uptake
- Assuming tap water provides enough
Key takeaways
- Formula: Mg fertilizer (g) = Target Mg PPM × Volume (L) ÷ 1,000 ÷ Mg fraction
- Remember: Common Mg sources.
- Watch out for: High K blocking Mg uptake
- Next step: run your own numbers in the calculator above, then verify with a measurement — calculated values are only as good as the inputs.
Frequently asked questions
What magnesium PPM for hydroponics?
30–70 PPM.
Can I use Epsom salt?
Yes — it is 9.8% magnesium.